Recent Anthropogenic Impacts on the Bilbao Estuary, Northern Spain: Geochemical and Microfaunal Evidence

Abstract

The distributions of a range of elements (including137Cs and210Pb) have been studied in surface sediments and 0·5m cores from the Bilbao Estuary (Cantabrian coast, northern Spain) to determine recent and historical sediment contamination. Benthic foraminifera have also been examined to infer recent ecosystem changes. High concentrations of a range of metals are observed in three cores and in surface-scrapes. Observed concentrations depend on the proximity to sources of pollutants. Living foraminifera are absent from surface sediments in the upper estuary, and are scarce in the middle and lower estuary, due to persistent anoxia in the estuarine channel, and possibly, high pollutant concentrations. High metal concentrations in sediment core profiles, combined with the sporadic presence of foraminifera, indicate that environmental degradation has persisted in this estuary for at least the last 40 years. This degradation has been caused by the discharge of untreated industrial and domestic effluents. Surface sediments show a few transported living foraminifera of species that have been identified as dominant in nearby, less-polluted estuarine environments. Successful recolonization by these species may occur if the sediment conditions improve sufficiently. Foraminiferal assemblages could therefore be used as environmental quality indicators to assess the effectiveness of current regeneration schemes implemented under strategic local authority plans.